Heretofore, others have provided main frames for side loader trucks such as are illustrated in U.S. Pat. Nos. 2,621,812; 3,712,492; 3,735,885; and 3,756,437. The bridge between the front and rear sections of a side loader must be capable of resisting considerable torsional loads. At the same time it is desired to keep the bridge structure relatively narrow in its lateral width so as to permit the traversing mast to retract sufficiently far to fully utilize the decks on the front and rear sections for supporting the payload.